894 REPORT OF COMMISSIONER OF FISH AXD FISHERIES. [4] 



front part of the bodj", while opposite (therefore at the posterior part) 

 the hinge is found. The central mass becomes more clearly defined, 

 and is separated from the ectoderm by a certain space. Later, the two 

 valves of the shell become visible round the hind part of the body. 

 The central mass is divided into two parts, one of which, of a darker 

 color, perhaps corresponds to the liver, while the other, which begins 

 to exhibit dilating and contracting movements, becomes the intestinal 

 canal. The shell of these embryos is already composed of a calcareous 

 substance. 



While the embryo continues to grow the ciliary apparatus increases 

 in dimensions, so that it seems to form, so to speak, a separate organ 

 from the rest of the bod}', by means of which the embryo can swim in 

 any direction. Gradually the basis of the ciliary ai)paratus decreases 

 in size, so that finally it is attached to the body only by a thin stem, 

 which breaks in due time. The ciliary apparatus which thus becomes 

 detached has the shape of a round cushion, having in the center an 

 opening which corresponds to the mouth aperture. The digestive canal 

 assumes the shape of a retort, inclosing the liver in its concave part; 

 the wide part of the retort forms the stomach, and the narrow part the 

 intestines, which, owing to their general development, elongate and 

 form a loop, which is i:)lainly visible. Davaine was not able to observe 

 with any degree of certainty either the mouth or the anus or the 

 organs of sight and hearing. The api^earance of the branchia is indi- 

 cated by a very distinct vibratile movement on the sid(i of the body. 

 At the same time there was observed below the mouth aperture a 

 small pear-shaped and transparent organ, the rapid pulsations of 

 wdiich show that it is the heart. The embryos probably remain in the 

 mantle cavity of the mother oyster more than a month. Their num- 

 ber in a good- sized oyster has been estimated at 1,125,000. 



De Lacaze-Duthiers^ (1854), who, after Davaine, had occupied himself 

 during two summers with the study of the development of the oyster, 

 has in several respects continued and completed the observations of 

 his predecessor. 



1. The oyster is a hermaphrodite. Fecundation takes place in the 

 efferent canals of the genital gland, and segmentation commences 

 immediately after the eggs have been set free. The egg is generally 

 divided into four, sometimes two, and rarely three segmentation 

 spheres. From these first four spheres there are formed, as it were by 

 a budding process, small transparent hyaline spherules, which increase 

 so as soon to cover entirely the dark and granular spheres forming the 

 vitellus, so much so that soon there can be distinguished in the egg a 

 peripheral and a central portion ; the embryo then becomes heart, 

 shaped ; at the depression which corresponds to the dorsal part there 



^ H. De Lacaze-Duthiers : Mimoire siir le developpement des Ac^phales LamelUhranches 

 (Ostrea) in Comptes Eendus de VAc. de Sc. Paris, vol. xxxix, p. 103. Also JVbit- 

 velles observations sur le developpement des huitres, same work, p. 1197. 



